1. Field of the Invention
The present invention relates to tensionable cable bolts, in particular, a tensionable cable bolt which is adapted to be resin grouted and mechanically anchored in a mine roof bore hole and a method of manufacturing same.
2. Description of Related Art
Cable bolts are used in the mining industry for their ease of handling and installation. Cable bolts are substantially easier to fit into a bore hole than the elongated rods of conventional rod bolt systems. Regardless of the height limitations in a mine, cable bolts may be adapted to bore holes of any length due to their flexibility. The strength capacity of cables exceeds that of conventional rod bolts and, therefore, cable is the preferred reinforcement for certain roof conditions.
Conventional cable bolts are installed by placing a resin cartridge including catalyst and adhesive material into the blind end of a bore hole, inserting the cable bolt into the bore hole so that the upper end of the cable bolt rips open the resin cartridge and the resin flows in the annulus between the bore hole and the cable bolt, rotating the cable bolt to mix the resin catalyst and adhesive, and allowing the resin to set about the cable bolt.
Tensionable cable bolts are the subject of U.S. Pat. No. 5,378,087 to Locotos and U.S. Pat. No. 5,525,013 to Seegmiller et al. Each of the bolts described therein is resin grouted at the blind end of a bore hole and, following setting of the resin, they are tensioned by rotation of a nut on an externally-threaded shaft surrounding the free end of the cable. U.S. Pat. No. 5,531,545 to Seegmiller et al. and U.S. Pat. No. 5,556,233 to Kovago both disclose tensionable bolts with a mechanical anchor mounted on the upper end of the cable bolt and tensioning mechanisms disposed on their free ends for post-installation tensioning. These prior art cable bolts are tensionable and require two installation steps; namely, a first step to anchor the upper end of the cable bolt in the bore hole and a second step to tension the cable bolt.
The tensionable cable bolt described in U.S. Pat. No. 6,270,290 to Stankus et al. allows the resin mixing step and the tensioning to be achieved simultaneously. The cable bolt includes an elongated member having a mixing portion adapted to be resin grouted within a bore hole in rock and an anchoring portion adapted to be mechanically anchored to the rock. A drivehead is attached to a lower end of the elongated member. When resin is inserted into the bore hole and the drivehead is rotated, the mixing portion rotates and mixes the resin and the anchoring portion anchors to the rock. The mixing portion includes a plurality of birdcaged portions of the cable or similar mixing devices. The anchoring portion includes an externally-threaded shaft attached to the cable and a mechanical anchor threaded onto the threaded shaft. Generally, the shaft is hollow and is in the form of a sleeve through which the cable extends. The shaft may be crimped to the cable. Rotating the drivehead simultaneously rotates the resin mixing portion and the shaft resulting in mixing of the resin in the bore hole, and the threading of the mechanical anchor onto the shaft causing the mechanical anchor to expand and engage the rock, thereby tensioning the cable bolt.